Exploring Stellar Winds

byPaul GilsteronJune 29, 2011

We’ve often speculated about the potential uses of the solar wind in pushing a ‘magsail’ to high velocities for missions beyond the Solar System. This isn’t solar sailing of the conventional type, in which the transfer of momentum from solar photons is the operating force. Instead of photons, a magsail would rely on the solar wind’s stream of charged particles, which can reach speeds of up to 800 kilometers per second. One problem, of course, is that the solar wind varies hugely, variations that might make managing a magsail a daunting task. In any case, before we can contemplate such missions, we have much to learn about how the solar wind operates.

Not all of that work is going to focus on our own Sun. We’re also learning how stellar winds operate in other star systems through careful observation, as new work from the European Space Agency’s XMM-Newton space observatory reminds us. The spacecraft recently observed a flare during a scheduled 12.5-hour observation of a system known as IGR J18410-0535, where a neutron star and a blue supergiant are in close proximity. The flare, which at X-ray wavelengths was almost 10,000 times the star’s normal brightness, resulted from the neutron star trying to absorb an enormous clump of matter flung from its companion.

Enrico Bozzo (University of Geneva) says the flare was the result of ‘a huge bullet of gas that the star shot out,’ one that hit the neutron star, causing the gas in the clump to be heated to millions of degrees. Although expelling matter into space is a normal part of the stellar wind for all stars, the intensity of this particular X-ray flare shows that the blue supergiant star can release chunks of gaseous matter so large that most of it didn’t even hit the neutron star.

Without the nearby neutron star, such an event would not have been detectable from Earth, but with its help we can gain insight into the varied behavior of stellar wind patterns. The XMM-Newton spacecraft recorded the flare as lasting four hours, allowing astronomers to estimate the size of the clump of matter at some 16 million kilometers across, about 100 billion times the volume of the Moon, though containing only about 1/1000th of the Moon’s mass. The neutron star, thought to be about 10 kilometers in diameter, is the collapsed core of a once far larger star, now so dense that it generates a strong gravitational field. It now proves to be a useful detector for a stellar event of the kind we should be able to observe in other such systems.

We’ve taken useful measurements of our own star’s solar wind through the Ulysses and Advanced Composition Explorer spacecraft, not to mention the continuing work of our Voyagers as they study the solar wind’s behavior at the edge of the Solar System. Even with our own relatively stable star, we’ve learned that the solar wind is turbulent, with streams of material moving at different speeds and colliding to produce so-called Co-rotating Interactive Regions. Slower moving winds tend to come from regions overlying sunspots, while high-speed winds are associated with coronal holes, dark coronal regions often found at the Sun’s poles.

A slow-moving stream pushed by faster material behind it can produce shock waves that accelerate solar wind particles to high speeds, buffeting the Earth’s magnetic field and producing storms in our planet’s magnetosphere. We also find magnetic clouds produced when solar eruptions carry material off the Sun along with embedded magnetic fields (for more on all this, see this useful MSFC page on the solar wind). Now imagine trying to ride this wind using a magnetic bubble hundreds of kilometers in diameter — formed by injecting plasma into a magnetic field — as envisioned in Robert Winglee’s Mini-Magnetospheric Plasma Propulsion idea. Or take the idea a step further still, using a magsail to decelerate an interstellar probe by braking against the destination star’s stellar wind. The more we learn about how stars shed matter, the sooner we’ll discover how practical some of these concepts really are.

Image: Artist’s impression of a mini-magnetosphere deployed around a spacecraft. Plasma or ionized gas is trapped on the magnetic field lines generated onboard, and this plasma inflates the magnetic field much like hot air inflates a balloon. Credit: Robert Winglee.

Can magsails get their push from something other than the highly changeable solar wind? Dana Andrews (Andrews Space) has argued for some time that a magnetic sail could be pushed by a neutral plasma beam. That paper makes for fascinating reading. It’s “Interstellar Propulsion Opportunities Using Near-Term Technologies,” in Acta Astronautica Vol. 55 (2004), pp. 443-451. Robert Winglee (University of Washington) developed the Mini-Magnetospheric Plasma Propulsion concept in Phase I and II studies for NIAC. The Phase II study, “Mini-Magnetospheric Plasma Propulsion, M2P2” is particularly useful (full text). It is only one of a number of magsail concepts being investigated in the literature.

Comments on this entry are closed.

Mark PrescoJune 29, 2011, 11:46

Although I have brought this subject up before, I would like to know if it I feasible .

If a Dyson swarm is constructed to harness the total energy of the sun, could we collimate a beam of light to Alpha Centauri, using a swarm of lasers if necessary? By my calculations, a beam equivalent to the diameter of the earth with a solar flux density equal to that at 1 AU would require only one billionth of the total energy of the sun. This “light bridge” could not only propel a fleet of colony ships to Alpha Centauri, but would also supply all of the energy needed to sustain the voyage.

If there is a civilization out there using light bridges, it should be detectable by optical SETI.

As long as we’re musing about exploiting stellar winds,
how about harvesting them for rare elements?
This would enable space-based civilizations to settle
stars otherwise too marginal due to low orbital content.
I would expect Sirius and Procyon, as a matter of fact,
to have this problem, due to their white-dwarf remnants
indicating past stellar cataclysms by stars even bigger
than the current stars we designate ‘A’.

While Epsilon Eridani has the most promising dust signature,
and thus would be the first call for settlers from Sol,
nearby Sirus and Procyon may have nothing but dust,
and big stellar winds. Ditto for lone white dwarfs.

Are there studies about superconducting magnetic loops
on the scale of the Moon’s orbit?
A mega-scale mass spectrometer, with He3 as first prize.
That would be a cargo worth hauling across light-years,
unlike those silly (and impossible) military ‘vehicles’ in the Avatar movie.

I have a question (I am a layman in astrophysics… just a robotics engineer)… Wouldn’t a magsail/solar sail hybrid be a good Idea then? An interstellar mission would be a huge project- so I guess combining technologies to improve performance is not out of the question. Could this combination of propulsion methods squeeze a bigger fraction of ‘c’ out of a space craft?

Three years back, I emailed Pekka Johannen about how fast mag sail and electric sails could go. He thought that it could achieve 100km/sec maximum (25-30% of the speed of the solar wind). I understand that gusts can achieve up to 900 km/sec and I wonder if, during a gust, the density of the wind might be higher than average.

But even if you could get to 200km/sec, the travel time to Alpha Centauri would be something like 5,000 yrs – much too long for a science mission and probably too long to ensure viability of a colonization for insurance mission. Pekka suggested beamed propulsion instead of just the solar wind.

It’s been a long time, but I remember someone commenting (on another site I think) that the M2P2 has an Achilles heel being that the solar wind flowing past the inflated bubble would turn it into a comet-like shape and that at the tip of the tail, the plasma would peel off plasma and so the buble would deflate. Don’t know if this is true or not.

Imagine a 10 km diameter ultra light spun graphite fiber tube geodesic sphere assembled in LEO. The outside radius of the tubing is sputter coated with superconducting graphene. At each vertices a superconducting cable. The cables collectively suspend two structures in a web-like configuration. One structure contains a pressurized habitat and bridge. The other a nuclear powered MHD electrical generator. Power fed thru the cables is used to shape desired magnetic field(s) by energizing various patterns in the superconducting exterior structure of the geodesic sphere. Imagine hanging out at Earth’s Lagrange 2 for a suitable CME to pass thru… then ‘catching a wave’!

Hi John
Interesting datum. Pekka’s work also demonstrated the other related flaw of the M2P2 concept – the lack of a coupling between the plasma bubble and the vehicle, meaning the solar wind will strip it away. But plasma physics is tricky – as Pekka’s own work shows – and does surprising things in the wild that our theoretical and computational tools can’t yet handle in the detail we’d like. Maybe there’s someway of improving a plasma sail’s performance, or even restocking the stripped plasma from the beam or wind impinging on it.

Clockwork Eric, the Dana Andrews paper referenced above examines such a concept and it has been studied by other researchers. Doesn’t necessarily enhance the speed, but does allow the two to complement each other.

Interstellar Bill, nice idea. Currently under investigation for our Sun.

Mark Presco, that’s one more super-technology to spot ETI activity by. Getting to be quite a list.

It does not seem a very attractive proposition to gather highly dilute matter from the solar wind when there is much more of it already conveniently lumped together in the form of planets, moons, asteroids, KBO’s and the like.

Mark Presco, assuming that your aim is to maximise scientific interest, rather than minimising criticism, I fear that you have fallen into a trap, that Karl Popper outlined rather better than I will here.

The essence of science is to compare various models against each other, to which purpose the clearer and more clean cut the prediction the better. You have mixed your earlier idea of using mirrors to provide light and propulsion, and the much better examined potential for lasers. Such a mix makes your model far more flexible, thus attracting less criticism, but without weaknesses there can be no more than arbitrary interest.

Your previous model had many pitfalls, but you shouldn’t just think of these as weaknesses. I had written, and still maintain, that the only circumstances that would seem to convey plausibility to your original idea was around O and B stars a few thousand years before the supernova. This is not nearly so bad as it sounds since it has previously been postulated that, if truly advanced civilisations have only an order of magnitude more difficulty travelling hundreds of light years than a few dozen, and are good at shielding themselves from radiation, then it would make sense if they were only interested in colonising O and B stars.

If you model is restricted to this rare type of star within a narrow epoch this would also be good news. With so few targets the possibility that your idea might attract interest becomes higher, not lower.

Strange as it may seem, for scientific purposes, even giving up is better than compromise. Also, in reality the best solutions usually come from one extremity or the other rather than a compromise.

Magnetic Fields in Earth-like Exoplanets and Implications for Habitability around M-dwarfs

Mercedes Lopez-Morales, Natalia Gomez-Perez, Thomas Ruedas

(Submitted on 14 Jul 2011)

We present estimations of dipolar magnetic moments for terrestrial exoplanets using the Olson & Christiansen (2006) scaling law and assuming their interior structure is similar to Earth. We find that the dipolar moment of fast rotating planets (where the Coriolis force dominates convection in the core), may amount up to ~80 times the magnetic moment of Earth, M_Earth, for at least part of the planets’ lifetime. For very slow rotating planets (where the force of inertia dominates), the dipolar magnetic moment only reaches up to ~1.5 M_Earth.

Applying our calculations to currently confirmed rocky exoplanets, we find that CoRoT-7b, Kepler-10b and 55 Cnc e can sustain dynamos up to ~ 18, 15 and 13 M_Earth, respectively.

Our results also indicate that the magnetic moment of rocky exoplanets not only depends on their rotation rate, but also on their formation history, thermal state, age and composition, as well as the geometry of the field. These results apply to all rocky planets, but have important implications for the particular case of exoplanets in the Habitable Zone of M-dwarfs.

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last twelve years, this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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